Electrostatic chuck power supply

ABSTRACT

A detection circuit is provided for a power supply for an electrostatic chuck generating a trapezoidal waveform with approximately flat tops and minimal dead-time between phase reversals. The detection circuit includes an amplifying circuit which receives inputs from a secondary winding of a transformer of the power supply and produces an amplified buffered signal. A chucking detect circuit receives the signal from the amplifying circuit and is configured to produce a first signal indicative of a substrate on the electrostatic chuck and a second signal indicative of an electrostatic chuck without a substrate. A chucking quality circuit receives the signal from the amplifying circuit and produces a signal indicative of a quality of the chucking of the substrate. A movement detection circuit receives the signal from the amplifying circuit and produces a signal indicative of movement of the substrate on the electrostatic chuck.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation-in-part of U.S. application Ser. No.12/208,404, entitled “Electrostatic Chuck Power Supply”, filed Sep. 11,2008, the disclosure of which is hereby incorporated by reference in itsentirety.

FIELD OF THE INVENTION

The invention relates generally to electrostatic chucks for holding asubstrate and in particular a detection of the substrate on theelectrostatic chuck.

BACKGROUND OF THE INVENTION

Recently, in the semiconductor industry, advanced processing techniques,such as CVD, dry etching, or gas cluster ion beam processing in a vacuumenvironment, are commonly used in the semiconductor manufacturingprocess. It is extremely challenging, if not nearly impossible, to use avacuum chuck to hold a semiconductor wafer or other substrate in avacuum chamber. Some contemporary solutions to this problem generallyinclude mechanical holding systems that hold substrates made fromsemiconducting materials, typically silicon or silicon-containingmaterials, at their periphery. However, silicon wafers, for example, areextremely brittle and there is always some risk of tiny pieces chippingoff of the semiconductor, or other substrate when using a mechanicalholding system. Generating such small dust particles from the chippingmay result in serious problems for the quality of production andpotentially affect yield rate.

Semiconductor processing equipment, therefore, has increasingly reliedupon the use of electrostatic clamping methods for holding substrates inplace while processing, rather than mechanical clamping methods. Theadvantages of using electrostatic clamping methods generally includefewer particles being generated and, in some cases, simplified clampinghardware. In the effort to reduce particles in the vacuum, it is alsodesirable to have as few in-vacuum connections and components.

Contemporary electrostatic chuck designs are of either DC or ACconfigurations, and generally comprise one, two, or more poles. Thechucks typically comprise a dielectric ceramic layer, or similardielectric material, with the poles comprising a conductive materialjust below the clamping surface. High voltages are applied to a singlepole, or pole-to-pole, relying on field changes in the dielectric layereffecting opposite field changes in the substrate, resulting inelectrostatic forces to hold the substrate to the chuck.

The clamping force is directly proportional to the dielectric constantand the net pole voltage difference, and inversely proportional to thedielectric thickness. Therefore, the thinner the dielectric, the higherthe clamping force. As higher through-put demands require higher-speedscanning, higher inertial forces are generated requiring higher clampingforces. Thus, it is desirable to have a chuck with the thinnestdielectric possible. However, one tradeoff to a thin dielectric is thevoltage breakdown through it.

With AC chucks, a sinusoidal voltage waveform will have to have a peakvoltage of about 1.4 times the desired clamping voltage in order toattain the same average force if DC was used instead. The peak-to-peakvoltages required for AC chucks can become problematic for chucks withthin dielectrics as the peak voltages necessary for required clampingforces approach the breakdown voltages of the dielectric. DC chucks alsooften require phase reversal and decaying AC fields in order todischarge the net field, otherwise the substrate would never de-chuck.

With DC chucks, contemporary power supplies require an external floatingsignal super-imposed onto the high-voltage chuck signals, usingfrequency-to-voltage techniques to create a substrate present signal inorder to test for presence of a substrate on the chuck. This techniquerequires extra components and sensors in the vacuum, which areundesirable as they are a potential source of particles in the vacuum.Also, this technique may not work with an AC output.

What is needed therefore is a power supply for an electrostatic chuckthat can provide AC power to an AC chuck without the concern of thepeak-to-peak voltage and be able to detect the presence of a substrateon either an AC or a DC chuck.

SUMMARY OF THE INVENTION

Embodiments of a detection circuit for a power supply for anelectrostatic chuck are provided. The power supply may include a signalgenerating circuit configured to generate an input, a power outputcircuit configured to produce a signal for the electrostatic chuck inresponse to the input signal, and a feedback circuit electricallyconnected to the power circuit and configured to feed back a voltagesignal responsive to a voltage on the electrostatic chuck. The signalfrom the power output circuit may be a trapezoidal waveform withapproximately flat tops and minimal dead-time between phase reversals.The detection circuit may be electrically connected to the electrostaticchuck through the feedback circuit of the power supply and includes, insome embodiments, an amplifying circuit receiving inputs from the poweroutput circuit and producing an amplified buffered signal, a chuckingquality circuit receiving the signal from the amplifying circuit, andconfigured to produce a signal indicative of a quality of a chuckedsubstrate, and a movement detection circuit receiving the signal fromthe amplifying circuit, and configured to produce a signal indicative ofmovement of the substrate on the chuck.

In some embodiments, the detection circuit may further include achucking detect circuit which receives the signal from the amplifyingcircuit and is configured to produce a first signal indicative of asubstrate on the chuck and a second signal indicative of a chuck withouta substrate. In some configurations of the detection circuit, thechucking quality circuit may include a circuit configured to rectify andfilter the amplified buffered signal producing a DC output, where anincreasing DC value in the DC output indicates a decrease in chuckingquality. In other configurations of the detection circuit, the movementdetection circuit may include a circuit configured to calibrate theamplified buffered signal with a threshold voltage, and a pulsestretcher configured to produce a signal representative of a shortduration pulse, but having a duration greater than the short durationpulse, in response to a triggering event. In a specific embodiment, thepulse stretcher may be a one-shot. In some embodiments, the pulsestretcher may be triggered on a rising edge of the amplified bufferedsignal, though a trailing edge may also be used in some embodiments.

Some embodiments include a semiconductor processing system. Theprocessing system may include an electrostatic chuck and a power supply.The power supply may include a signal generating circuit configured togenerate an input, a power output circuit configured to produce a signalfor the electrostatic chuck in response to the input signal, a feedbackcircuit electrically connected to the power circuit and configured tofeed back a voltage signal responsive to a voltage on the electrostaticchuck, and a detection circuit electrically connected to theelectrostatic chuck, through the feedback circuit and configured tointerpret the voltage signal and to produce an output signal indicativeof a condition of a substrate on the electrostatic chuck.

In some embodiments, the signal from the secondary winding may be atrapezoidal waveform with approximately flat tops and minimal dead-timebetween phase reversals. In some embodiments, the detection circuit mayinclude an amplifying circuit receiving inputs from the secondarywinding and producing an amplified buffered signal, and a chuckingdetect circuit receiving the signal from the amplifying circuit, andconfigured to produce a first signal indicative of a substrate on thechuck and a second signal indicative of a chuck without a substrate.

In other embodiments, the detection circuit may include the amplifyingcircuit receiving inputs from the secondary winding and producing anamplified buffered signal and a chucking quality circuit receiving thesignal from the amplifying circuit and producing a signal indicative ofa quality of a chucked substrate. In some of these embodiments, thechucking quality circuit may include a circuit configured to rectify andfilter the amplified buffered signal producing a DC output. In theseembodiments, an increasing DC value in the DC output may indicate adecrease in chucking quality.

In some embodiments the detection circuit may include the amplifyingcircuit receiving inputs from the secondary winding and producing anamplified buffered signal and a movement detection circuit whichreceives the signal from the amplifying circuit produces a signalindicative of movement of the substrate on the chuck. In theseembodiments, the movement detection circuit may include a circuitconfigured to calibrate the amplified buffered signal with a thresholdvoltage and a pulse stretcher configured to produce a signalrepresentative of a short duration pulse, which has a duration greaterthan the short duration pulse. In a specific embodiment, the pulsestretcher may include a one-shot. In another specific embodiment, thepulse stretcher may be triggered on a rising edge of the amplifiedbuffered signal.

Embodiments of also provide a method of detecting a condition of asubstrate on an electrostatic chuck in a processing apparatus. A voltagemay be sensed on an output of a power supply connected to theelectrostatic chuck for supplying a chucking voltage to the chuckthrough a feedback circuit. A change in the sensed voltage may bedetected which is indicative of a change of a condition of the substrateon the chuck. An operation of the processing apparatus may then becontrolled in response to detecting the change in sensed voltage.

In some embodiments, sensing the voltage on the output of the powersupply may include filtering and buffering the voltage to generate a DCvoltage. In some of these embodiments, the detected change in the sensedvoltage may include an increasing DC value and the change of thecondition may include an increase in buildup of material between thechuck and the substrate. In these embodiments, the operation may includeinitiating a cleaning or replacement of the chuck. In other embodiments,sensing the voltage on the output of the power supply may includecalibrating the voltage on the output of the power supply with areference voltage and detecting a change in the sensed voltage mayinclude detecting a short duration pulse in the voltage on the output ofthe power supply that exceeds the reference voltage, and generating asignal representative of a short duration pulse with a pulse stretcherhaving a duration greater than the short duration pulse. In someembodiment, the change of the condition may be a movement of thesubstrate on the chuck.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are incorporated in and constitute apart of this specification, illustrate embodiments of the invention and,together with a general description of the invention given above, andthe detailed description given below, serve to explain the invention.

FIG. 1 is a cross-sectional view of an exemplary electrostatic chuck.

FIG. 2 is a system block diagram of an embodiment of the power supplyconsistent with the invention for use with the electrostatic chuck inFIG. 1.

FIG. 3 is a flowchart of the logic of the digital circuitry of thesystem block diagram in FIG. 2.

FIG. 4 is a schematic diagram of several of the components in the systemblock diagram in FIG. 2.

FIG. 5A is a graph of a signal applied to a primary winding of atransformer in the system block diagram in FIG. 2.

FIG. 5B is a graph of a second signal applied to the primary winding ofthe transformer in the system block diagram in FIG. 2.

FIG. 6 is a graph of the output signal from the secondary winding of thetransformer in the system block diagram in FIG. 2.

FIG. 7 is a graph of the ripple voltage output from a component in thesystem block diagram in FIG. 2.

FIG. 8 is a schematic diagram of several of the components of the rippledetection circuitry of FIG. 2.

FIG. 9 is a graph illustrating an output of the chuck detect circuit ofFIG. 8

FIG. 10 is a graph illustrating filtered and unfiltered signalsrepresenting chucking quality.

FIG. 11 is a graph illustrating pulse stretching of an unfiltered signalrepresenting chucking quality.

FIG. 12A is a graph illustrating a pulse stretcher being continuallyretriggered.

FIG. 12B is a graph illustrating a pulse stretcher responsive to asingle trigger event.

FIG. 12C is a graph illustrating a pulse stretcher response to multipletrigger events.

It should be understood that the appended drawings are not necessarilyto scale, presenting a somewhat simplified representation of variousfeatures illustrative of the basic principles of the invention. Thespecific design features of the sequence of operations as disclosedherein, including, for example, specific dimensions, orientations,locations, and shapes of various illustrated components, will bedetermined in part by the particular intended application and useenvironment. Certain features of the illustrated embodiments have beenenlarged or distorted relative to others to facilitate visualization andclear understanding. In particular, thin features may be thickened, forexample, for clarity or illustration.

DETAILED DESCRIPTION OF THE INVENTION

Embodiments of the invention generate trapezoidal waveforms withessentially flat tops and minimal dead-time between phase reversals forAC electrostatic chucks without the concern of peak voltages as withsinusoidal or triangular waveforms. The output of the embodiments of theinvention may be changed from AC to DC. This may even be accomplishedwhile the power supply is running. Additionally, in DC mode, a change inan output voltage ripple may be used to detect the presence of asubstrate on the chuck. Similarly, in AC mode, a change in an outputcurrent ripple may be used to detect the presence of the substrate onthe chuck.

Turning now to the drawings, FIG. 1 is a cross sectional diagram of anexemplary DC electrostatic chuck 10. Electrostatic chucks 10 generallyhave the structure of a capacitor, which includes two electrodesadjacent to a dielectric 12. One of the electrodes is the object on thechuck, here, a semiconductor substrate 14, such as a silicon wafer.While reference is made to a semiconductor substrate such as the siliconwafer, it should be understood that the invention should not be solimited, but rather, the “object” may be any substrate 14, including,for example, glass panels for displays, substrates for hard diskmagnetic heads, substrates from which optical components aremanufactured, etc. The other of the electrodes in FIG. 1 areinterdigitated electrodes 16, 18. When the interdigitated electrodes 16,18 are employed and a high voltage source 20 is applied, an equivalentcircuit for the electrostatic chuck 10 would be a series connection oftwo capacitors. Because the conductivity of substrate 14 (e.g. siliconwafer) is much higher than the dielectric 12, the substrate 14 isassumed to be a conductor.

The fundamental structure of the electrostatic chuck 10 is schematicallyshown in FIG. 1. The main part of the electrostatic chuck 10 includesinterdigitated electrodes 16, 18 and the dielectric 12. Theinterdigitated electrodes 16, 18 may be created from an etched printedcircuit board by removing copper film, though other conductive films mayalso be used. The dielectric 12 is placed over the interdigitatedelectrodes 16, 18. Since the thickness of a copper sheet is generallyabout 35 μm, there may be an air gap between the interdigitatedelectrodes 16, 18 of the same size. In order to avoid a spark dischargebetween the interdigitated electrodes 16, 18, the space is filled withan insulating material 22.

Because the potential of the substrate 14 could be the ground level, onehigh voltage source 20 is employed in the exemplary electrostatic chuck10 in FIG. 1 for simplicity. However, multiple voltage sources, i.e. twoin this example, could also be used. If the likelihood for the substrate14 to be grounded is low, one high-voltage source may actually bepreferable, especially in the case of AC applied voltages.

A system diagram in FIG. 2 shows the components of an electrostaticpower supply 30 consistent with embodiments of the invention. The powersupply 30 generally includes control inputs and outputs 32, a signalgenerating circuit 34, a power amplification stage 36 with feedback 38,transformers 40, and an AC/DC switch or rectifier 42 which sends theamplified signals to an electrostatic chuck 10. The power supply 30additionally includes ripple detection circuitry 44, which may be usedto determine if a substrate 14 is present on the electrostatic chuck 10.Additionally the ripple detection circuitry 44 may also be used, in someembodiments, to detect slipping or other movement of the substrate 14 onthe electrostatic chuck 10 or overall chucking quality, as will bedescribed in more detail below. In some embodiments, the controlinputs/outputs 32 of power supply 30 include two inputs: an analogcontrol input 46 and a digital control input 48. The analog controlinput 46 is an amplitude adjustment, which allows for a peak-to-peakvoltage adjustment of the power supply 30. The digital control input 48is a digital signal indicating that a substrate 14 is to be placed onthe electrostatic chuck 10. In some embodiments, the digital signal forthe digital control input 48 may be a “CHUCK” signal to indicate whetheran electrostatic chuck 10 is enabled and whether a substrate 14 shouldbe placed on the electrostatic chuck 10. In some embodiments, thecontrol inputs/outputs 32 of power supply 30 include a digital controloutput 50 that provides two signals. One of the signals may be a“CHUCKED” signal to indicate that a substrate 14 is present on theelectrostatic chuck 10. The other signal may be a “CHUCK FLT” signal toindicate a fault in the chucking process, which will be discussed infurther detail below. The control inputs/outputs 32 of power supply 30may further include an analog control output 52, which may also providetwo signals. These two signals may be used to determine slip of thesubstrate 14 on the electrostatic chuck 10. Additionally, these twosignals may be used to determine substrate-to-substrate chucking qualityby analyzing deterioration, over time, of the chuck force, facilitatinganticipation of necessary periodic maintenance or prediction of failure.

Digital components 54 of the power supply 30, including the digitalcontrol input 48 and the digital control output 50, may be implementedaccording to the flowchart 60 in FIG. 3. A check of the CHUCKED outputsignal is made to determine if a substrate 14 is present on theelectrostatic chuck 10 (block 62). If the CHUCKED output signalindicates that there is no substrate 14 present on the electrostaticchuck 10 (“No” branch of decision block 62), then a check is made to seeif the electrostatic chuck 10 is enabled to receive a substrate 14(block 64). If the CHUCK input signal indicates that the electrostaticchuck 10 is not enabled (“No” branch of decision block 64), then theprocess continues at decision block 62. If, however, the CHUCK inputsignal indicates that the electrostatic chuck 10 is enabled and shouldhave a substrate 14 present (“Yes” branch of decision block 64), theCHUCK FLT bit is turned on indicating a chucking fault (block 66). TheCHUCK FLT output may sent to a controller of a system utilizing theelectrostatic chuck 10 (block 68), which may then take further action,such as retrying a substrate delivery and chucking process, notifying anoperator for manual intervention, shutting down the system, or otheractions that would be known to one of ordinary skill in the art.

If there is a substrate 14 present on the electrostatic chuck 10 (“Yes”branch of decision block 62), the CHUCKED bit is turned on to indicatethe presence of the substrate 14 (block 70). A check is then made todetermine if the electrostatic chuck 10 is enabled to receive asubstrate 14 (block 72). If the CHUCK input signal indicates that theelectrostatic chuck 10 is not enabled (“No” branch of decision block 72)and there is a substrate 14 present, the CHUCK FLT bit is turned onindicating a chucking fault (block 66) and the process continues asdisclosed above. If, however, the CHUCK input signal indicates that theelectrostatic chuck 10 is enabled (“Yes” branch of decision block 72),then a check may be performed to determine if the substrate 14 isslipping (block 74). If there is an indication that the substrate 14 isslipping (“Yes” branch of decision block 74), then the slippinginformation may be communicated to the system controller (block 68) andfurther action may be taken. If there is no indication of the substrate14 slipping (“No” branch of decision block 74), a substrate-chuckquality may be reported (block 76) and the process continues at decisionblock 62. In some embodiments, the substrate-chuck quality may also becommunicated to the controller (block 68). In other embodiments, areport of substrate-chuck quality (block 76) may also be performed ifthe substrate 14 is slipping (not shown).

The input CHUCK signal and output CHUCKED and CHUCK FLT signals may beimplemented such that when the signals are high, they indicate apositive condition of the signal. In alternate embodiments, the CHUCK,CHUCKED, and CHUCK FLT signals may also be implemented such that thesignals indicate a positive condition when they are pulled low. One ofordinary skill in the art will recognize that any combinations of highor low may be used for any of the digital input or output signalswithout departing from the scope of the invention.

Returning again to FIG. 2, the signal generating circuit 34 includes ananalog voltage control 78, square wave generator 80, and an analog todigital signal converter 82, which may be used to convert analog signalsto the digital control output 50. Outputs from the analog voltagecontrol 78 and square wave generator 80 may be summed in a summingcircuit 84 prior to being sent to the power amplification stage 36. Thesquare wave generator 80 may be an XR-2207 Monolithic Function Generatormanufactured by Exar Corporation of Fremont, Calif., though any wavegenerator able to generate a square wave may be used. This particularsquare wave generator 80 has an operating frequency from about zero Hzto about 1 MHz. However, the magnitude of ripple current or ripplevoltage that is used for determining the presence or absence of asubstrate 14 decreases as frequency increases. Therefore, lowerfrequencies may be used to produce a peak-to-peak ripple thatadvantageously makes sensing easier. An exemplary operating frequencyrange may be from about 30 Hz to about 100 Hz, though higher frequenciesmay be used. For many embodiments, the typical operating frequency is inthe range of about 30 Hz to about 40 Hz.

The square wave output of the signal generating circuit 34 is sent tothe power amplification stage 36. The power amplification stage 36contains an amplifying circuit 86, 88, 90 corresponding to each of aplurality of poles of the electrostatic chuck 10. Many DC electrostaticchucks are monopolar, though they may also have multiple poles. ACelectrostatic chucks are generally bipolar and higher. Each pole of theAC or DC chuck may be driven by separate amplifying circuits 86, 88, 90.The embodiment illustrated in the system diagram in FIG. 2 consists ofthree poles. One of ordinary skill in the art will recognize that thenumber of poles is a property of the electrostatic chuck 10 and that thepower supply 30 may be designed to include a proper number of amplifyingcircuits 86, 88, 90 to match the number of poles for the electrostaticchuck 10 it is driving.

FIG. 4 provides additional detail for an amplifying circuit 86 of thepower amplification stage 36. The amplifying circuit 86 includes a firstamplifier 92 and a second amplifier 94. These amplifiers may be OPA541APhigh power monolithic operational amplifiers manufactured by TexasInstruments, though any suitable high power amplifiers may be used. Theinput to first amplifier 92 includes the square wave signal generatedfrom the square wave generator 80 in addition to a portion of the outputsignal 96 which is fed back to the power amplification stage 36. In aspecific embodiment, the first amplifier 92 amplifies the input to about40-60 volts. This output is sent through DC blocking capacitors 98 andthen to a first end 100 of a primary winding 102 of a transformer 104.The output is additionally sent to the input of the second amplifier 94,which also amplifies the input to about 40-60 volts. The output of thesecond amplifier 94 is sent to a second end 106 of the primary winding102 of the transformer 104. The two amplifiers 92, 94 are run counterphase in order to drive two times the signal on the primary winding 102of the transformer 104. FIG. 5A and FIG. 5B contain graphs of thewaveforms at the first end 100 and second end 106, respectively, of theprimary winding 102 of the transformer 104. As can also be seen from thegraphs in FIG. 5A and FIG. 5B, the maximum voltage, for this embodiment,applied to the primary winding 102 is about 100 V. In this embodiment,the turns ratio of the transformer 104 is about 10:1, though other turnsratios may be used in other embodiments to step up the voltage on asecondary winding 108 of the transformer 104 which is configured to beelectrically connected to the electrostatic chuck 10.

By applying the output waveforms of the amplifiers 92, 94 to ends 100,106 of the primary winding 102 of the transformer 104, the waveforms areeffectively summed. The resulting waveform on the secondary winding 108of the transformer 104 can be seen in the graph in FIG. 6. The maximumpeak-to-peak voltage of the output wave form on the secondary winding108 is about 1,000 V, though the output is fully adjustable from aboutzero to about 2,000 V peak-to-peak. The output voltage may be setappropriately to accommodate any dielectric material and thickness.

As can be seen in the graph in FIG. 6, the output waveform is generallytrapezoidal in shape with an essentially flat top. As also can be seenin the graph in FIG. 6, the output waveform also has short rise and falltimes, minimizing dead time between reversals. This trapezoidal waveformmay be applied directly from the secondary winding 108 of thetransformer 104 to one of the poles of an AC electrostatic chuck. In ACmode, the flat-topped waveforms allow for much higher RMS voltages thansinusoidal or triangular waveforms without the associated high peakvoltage stress. DC-like performance may also be attained using thistrapezoidal, AC output power supply. The trapezoidal output may berectified and then sent to one of the poles of the DC electrostaticchuck 10 as shown in FIG. 4, for example.

The signal from the secondary winding 108 is reduced by a voltagedivider 110 in order to reduce the signal to the portion of the outputsignal 96 to a manageable level in order to be fed back into the inputof the first amplifier 92. In a specific embodiment, the voltage isdivided down to 1/10 of the output to compensate for the 10:1 ratio ofthe transformer 104. In other embodiments, this voltage divider 110 maydivide the voltage differently to correspond to either a differenttransformer ratio or a larger or smaller feedback signal, which mayaffect the overall shape of the trapezoidal waveform. Additionally, thefeedback loop includes compensation capacitors 112 to preventoscillation and a transient voltage suppressor element 114 to protectfrom transients.

Referring again to FIG. 2, each amplifying circuit 86, 88, 90 in thepower amplification stage 36 has a corresponding transformer, i.e.amplifying circuit 86 to transformer 104, in the transformers 40. Eachof the outputs of the transformers 40 may be sent to the AC/DC switch 42to connect to either an AC or DC electrostatic chuck, as discussedabove. Additionally, a ripple may be detected on the output of thetransformers 40 by ripple detection circuitry 44 for each pole from thepower supply. This output (OUTPUT A 140 in FIG. 4) may also be furtherprocessed to determine overall chucking quality or to detect slippage orother movement of the substrate 14 on the electrostatic chuck 10 as setforth below. In AC mode, the output itself can also be used to sensewhether there is a substrate 14 present on an AC electrostatic chuck inthat during the rise-time of the power supply output (from thetransformers 40), the output current will rise proportionately inresponse to a capacitance change when the substrate 14 is clamped. Thiscurrent may then be used to determine the presence or absence of asubstrate 14 on the AC electrostatic chuck. In DC mode, if the output isleft unfiltered (as shown in FIG. 4), a power supply output ripple willbe present.

Once a substrate 14 has been clamped, output ripple falls due to theincrease in capacitance created by the substrate-plus-chuck interface.The DC ripple may be measured as a voltage across resistors 116-124 asshown in FIG. 4. FIG. 7 illustrates a change in magnitude of the ripplevoltage between a curve 130 representing ripple voltage for anelectrostatic chuck 10 with a substrate 14 present and a curve 132representing ripple voltage for an electrostatics chuck 10 without asubstrate 14. As set forth above, the operating frequency of the squarewave generator 80 may affect the magnitude of the ripple voltage andcurrents. Lower frequencies tend to produce larger differences in themagnitudes of the ripple voltages and currents, and thus tend to makemeasurements of those differences easier. The magnitudes of the ripplevoltages and currents may also be used to compare chucking quality fromsubstrate to substrate by comparing the magnitudes of the ripplevoltages, for example, from substrate to substrate. A higher ripplevoltage for a chucked substrate may indicate that the chuck is dirty andneeds to be cleaned, or that the chuck may need to be replaced. Themagnitude of the ripple voltage or current may also be monitored duringthe manufacturing process and may assist in detecting substrate slip onthe chuck.

More specifically, and as seen in FIG. 8, the outputs from the polesOUTPUT A 140 (also shown in FIG. 4) and OUTPUT B 142 from the powersupply are sent to an amplifying circuit 144. The amplifier circuit 144amplifies the signals from the opposite poles, buffers and then sums thesignals to provide a larger signal to the remainder of the rippledetection circuitry 44, which, in some embodiments, produces severaloutputs which can be seen in the graph in FIG. 9 and which will beaddressed in turn.

The amplified signal from the amplifier circuit is rectified andcompared to a reference signal 146 to produce a “high” or “low”indication of a substrate 14 present on the electrostatic chuck 10. Thechuck detect 148 signal, as seen in the curve 148 a in the graph 150 inFIG. 9, provides a “high” signal output when a substrate 14 is presenton the electrostatic chuck 10. In the graph 150, area 152 of curve 148 ashows a signal produced indicating a substrate 14 on the chuck. When thesubstrate is removed, represented by area 154 of curve 148 a, the signaldrops to a “low”.

A chuck quality signal 156 is taken prior to the comparison to thereference for the chucking detection and is heavily filtered to a DCoutput 156. This DC output may assist in monitoring the quality of thechucking process. As seen in the graph 158 in FIG. 10, an unfilteredchucking quality signal is represented by curve 160. The area 162 ofcurve 160 shows a series of uniform spikes indicating that a substrate14 is present on the electrostatic chuck 10. However, as can be seen inthe area 164 of curve 160, as the substrate 14 moves, the ripple voltagegreatly increases as illustrated by the spikes such as 166. By filteringthese signals, represented by curve 156 a, a measure of chucking qualitycan be monitored. As also seen in the area 164 of curve 156 a, as themovement of the substrate settles, the chucking quality signal does notreturn to its previous value, but rather indicates an increase, or lossof chucking quality. This may result from particles from the substrate14 being left behind on the electrostatic chuck 10 due to movement ofthe chuck or other outside contaminants, which may affect the chuckingquality of subsequent substrates 14. As the chucking quality value 156continues to increase, the quality decreases and at some point, theelectrostatic chuck 10 will need to either be cleaned or replaced. Itshould be noted, though, while the signals produced may indicate to anoperator or technician that the electrostatic chuck 10 needs some typeof attention, these signals are not high enough to produce a CHUCK FLTsignal.

The unfiltered signal may also be used to detect movement indicatingslippage or bouncing/flexing of the substrate 14. The detection circuitfor the fast moving peak utilizes the ripple signal directly from theamplifier circuit 144. This signal is calibrated with a referencethreshold 168 to filter out noise type spikes that may incorrectly beinterpreted a substrate 14 movement. The resulting signal is sentthrough a pulse stretcher 170, such as a one-shot, to facilitaterecognition of the slippage or other movement. The pulse stretcher 170can be configured in a non-retriggerable or a retriggerable mode onrising edges. The output may then be sent to an opto-coupler 172 in someembodiments, or other transmission medium in other embodiments.

Graph 174 in FIG. 11 shows the threshold 168 a level as well as thetriggered and extended pulse 176 indicating slippage or other movementof the substrate 14. FIGS. 12A-C show additional examples of the pulsestretching. Graph 178 in FIG. 12A illustrates a long chucking problem,where the curve 180 shows the pulse stretcher 170 being continuallyretriggered. Graph 182 in FIG. 12B illustrates a single event chuckingproblem, such as a slip or bounce, with one trigger of the pulsestretcher 170. As illustrated by curve 184 in this case, the pulsestretcher times out after a predetermined period of time and is ready todetect another event. Graph 186 in FIG. 12C illustrates multiplechucking problems where the pulse stretcher 170 is triggered andretriggered, which can be seen on the curve 188. The time duration ofthe pulse stretcher 170 is control system driven with typical timesranging from approximately 100 ms to approximately 600 ms based on thecontrol loop drive time period, although other times may be used forother embodiments.

Low frequency, trapezoidal outputs reduce peak-voltage stresses, and theall-in-one approach utilizing the power supply output signals to bothclamp and detect the substrate assists in cost effectiveness, loweringparticle contamination, and adds reliability. Embodiments of theinvention take advantage of the output characteristics of thelow-frequency AC (or unfiltered DC) output stage to detect the presenceof a substrate and require no additional connections external to thepower supply, requiring no extra in-vacuum sensors or connections.Furthermore the indication of chucking quality from the ripple detectioncircuitry as well as the ability to detect slippage or other movement ofthe wafer can assist in providing better wafer to wafer consistency.

While the present invention has been illustrated by a description of oneor more embodiments thereof and while these embodiments have beendescribed in considerable detail, they are not intended to restrict orin any way limit the scope of the appended claims to such detail.Additional advantages and modifications will readily appear to thoseskilled in the art. The invention in its broader aspects is thereforenot limited to the specific details, representative apparatus andmethod, and illustrative examples shown and described. Accordingly,departures may be made from such details without departing from thescope of the general inventive concept.

1. A detection circuit for a power supply for an electrostatic chuck,the power supply having a signal generating circuit configured togenerate an input, a power output circuit configured to produce a signalfor the electrostatic chuck in response to the input signal, and afeedback circuit electrically connected to the power circuit andconfigured to feed back a voltage signal responsive to a voltage on theelectrostatic chuck, wherein the signal from the power output circuit isa trapezoidal waveform with approximately flat tops and minimaldead-time between phase reversals, the detection circuit electricallyconnected to the electrostatic chuck through the feedback circuit andcomprising: an amplifying circuit receiving inputs from the power outputcircuit and producing an amplified buffered signal; a chucking qualitycircuit receiving the signal from the amplifying circuit, and configuredto produce a signal indicative of a quality of a chucked substrate; anda movement detection circuit receiving the signal from the amplifyingcircuit, and configured to produce a signal indicative of movement ofthe substrate on the chuck.
 2. The detection circuit of claim 1, furthercomprising: a chucking detect circuit receiving the signal from theamplifying circuit, and configured to produce a first signal indicativeof a substrate on the chuck and a second signal indicative of a chuckwithout a substrate.
 3. The detection circuit of claim 1, wherein thechucking quality circuit comprises: a circuit configured to rectify andfilter the amplified buffered signal producing a DC output, wherein anincreasing DC value in the DC output indicates a decrease in chuckingquality.
 4. The detection circuit of claim 1, wherein the movementdetection circuit comprises: a circuit configured to calibrate theamplified buffered signal with a threshold voltage; and a pulsestretcher configured to produce a signal representative of a shortduration pulse, having a duration greater than the short duration pulse,in response to a triggering event.
 5. The detection circuit of claim 4,wherein the pulse stretcher comprises a one-shot.
 6. The detectioncircuit of claim 4, wherein the pulse stretcher is triggered on a risingedge of the amplified buffered signal.
 7. A power supply comprising thedetection circuit of claim 1, the power supply further comprising: asignal generating circuit configured to generate a square wave signal;an amplifying circuit electrically connected to the signal generatingcircuit configured to amplify the square wave signal; a transformerhaving a primary winding and a secondary winding, the primary windingelectrically connected to the amplifying circuit, and the secondarywinding configured to be electrically connected to said electrostaticchuck, the secondary winding producing a signal for said electrostaticchuck; and a voltage divider circuit electrically connected to thesecondary winding and further connected to the amplifying circuit, thevoltage divider circuit configured to reduce the voltage of the signalfor the electrostatic chuck and feed back the reduced voltage signal tothe amplifying circuit, wherein the signal from the secondary winding isa trapezoidal waveform with approximately flat tops and minimaldead-time between phase reversals.
 8. A system comprising the powersupply of claim 7, the system further comprising: an electrostaticchuck, wherein the signal from the secondary winding is applied to theelectrostatic chuck.
 9. A semiconductor processing system, comprising:an electrostatic chuck; and a power supply configured to provide powerto the electrostatic chuck, the power supply including: a signalgenerating circuit configured to generate an input; a power outputcircuit configured to produce a signal for the electrostatic chuck inresponse to the input signal; a feedback circuit electrically connectedto the power circuit and configured to feed back a voltage signalresponsive to a voltage on the electrostatic chuck; and a detectioncircuit electrically connected to the electrostatic chuck, through thefeedback circuit and configured to interpret the voltage signal and toproduce an output signal indicative of a condition of a substrate on theelectrostatic chuck.
 10. The semiconductor processing system of claim 9,wherein the signal from the secondary winding is a trapezoidal waveformwith approximately flat tops and minimal dead-time between phasereversals.
 11. The semiconductor processing system of claim 9, whereinthe detection circuit comprises: an amplifying circuit receiving inputsfrom the secondary winding and producing an amplified buffered signal;and a chucking detect circuit receiving the signal from the amplifyingcircuit, and configured to produce a first signal indicative of asubstrate on the chuck and a second signal indicative of a chuck withouta substrate.
 12. The semiconductor processing system of claim 9, whereinthe detection circuit comprises: an amplifying circuit receiving inputsfrom the secondary winding and producing an amplified buffered signal;and a chucking quality circuit receiving the signal from the amplifyingcircuit, and configured to produce a signal indicative of a quality of achucked substrate.
 13. The semiconductor processing system of claim 12,wherein the chucking quality circuit comprises: a circuit configured torectify and filter the amplified buffered signal producing a DC output,wherein an increasing DC value in the DC output indicates a decrease inchucking quality.
 14. The semiconductor processing system of claim 9,wherein the detection circuit comprises: an amplifying circuit receivinginputs from the secondary winding and producing an amplified bufferedsignal; and a movement detection circuit receiving the signal from theamplifying circuit, and configured to produce a signal indicative ofmovement of the substrate on the chuck.
 15. The semiconductor processingsystem of claim 14, wherein the movement detection circuit comprises: acircuit configured to calibrate the amplified buffered signal with athreshold voltage; and a pulse stretcher configured to produce a signalrepresentative of a short duration pulse, having a duration greater thanthe short duration pulse, in response to a triggering event.
 16. Thesemiconductor processing system of claim 15, wherein the pulse stretchercomprises a one-shot.
 17. The semiconductor processing system of claim15, wherein the pulse stretcher is triggered on a rising edge of theamplified buffered signal.
 18. A method of detecting a condition of asubstrate on an electrostatic chuck in a processing apparatus, themethod comprising: sensing a voltage on an output of a power supplyconnected to the electrostatic chuck for supplying a chucking voltage tothe chuck through a feedback circuit; detecting a change in the sensedvoltage indicative of a change of a condition of the substrate on thechuck; and controlling an operation of the processing apparatus inresponse to the detecting of the change in sensed voltage.
 19. Themethod of claim 18, wherein sensing the voltage on the output of thepower supply comprises: filtering and buffering the voltage to generatea DC voltage.
 20. The method of claim 19, wherein the detected change inthe sensed voltage comprises an increasing DC value, the change of thecondition comprises an increase in buildup of material between the chuckand the substrate, and the operation comprises initiating a cleaning orreplacement of the chuck.
 21. The method of claim 18, wherein sensingthe voltage on the output of the power supply comprises calibrating thevoltage on the output of the power supply with a reference voltage andwherein detecting a change in the sensed voltage comprises: detecting ashort duration pulse in the voltage on the output of the power supplythat exceeds the reference voltage; and generating a signalrepresentative of a short duration pulse with a pulse stretcher having aduration greater than the short duration pulse.
 22. The method of claim21, wherein the change of the condition is a movement of the substrateon the chuck.